<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
    <style>
        .fade-enter,
        .fade-leave-to{
            opacity: 0;
        }
        .fade-enter-active,
        .fade-leave-active{
            transition: opacity 3s;
        }
    </style>
</head>
<body>
    <div id="root">
        <transition name="fade">
        <div v-if="show">hello world</div>
        </transition>
        <button @click="handleClick">切换</button>
    </div>
    <script>
        var vm=new Vue({
            el:'#root',
            data:{
                show:true
            },
            methods:{
                handleClick:function(){
                    this.show=!this.show
                }
            }
        })
    </script>
</body>
</html>